Fibrous substrates, such as paper and paperboard, are widely used in packaging operations. However, paper and paperboard can have very poor resistance to penetration by, for example, water vapor, gases, oils, solvents, and greases. To improve the resistance to penetration by such substances, paper and paperboard have been coated with a variety of materials. For many years, treatments with fluorochemicals, either by surface treatment or as a wet end additive in the paper making process, have been the dominant approach used to achieve oil and grease resistance (OGR) properties. Recent environmental concerns surrounding fluorochemicals, however, have prompted paper and paperboard manufacturers to search for alternative approaches to coating compositions that impart OGR properties to the coated paper.
Alternative approaches to impart OGR properties to coated paper have included using agents such as latexes, gelatins, starches, modified starches, and vegetable proteins. These agents, however, have been used in expensively large amounts in order to impart sufficient OGR properties. In addition, the use of such large amounts of these agents can result in treated paper and paperboard that is too stiff and/or brittle for many uses. As such, the coating materials can cause the coatings formed to fail when the coated paperboard or paper is creased and/or folded.
One approach to address the stiffness and/or brittleness of the coatings has been to incorporate high amounts of plasticizers into the coatings. While high amounts of plasticizer can help to increase the flexibility of the coatings, the high amounts of plasticizer can also result in a loss of oxygen barrier properties and a decrease in resistance to water vapor penetration, making the paper coatings ineffective for their intended purpose.
Accordingly, there is a continuing need for paper coatings that provide flexible barrier coatings on fibrous substrates having improved resistance to penetration by oil, grease, solvent, oxygen, and water vapor.